There is a magnetic disk device configured to execute processing of writing a servo pattern, for example, Self Servo Write (SSW). When writing a servo pattern by SSW, the magnetic disk device writes an experimental servo pattern on the disk. After writing the experimental servo pattern, the magnetic disk device detects a radial position of the disk at which the experimental servo pattern can optimally be read to thereby estimate an error of the track pitch. On the other hand, in recent years, a magnetic disk device of a Two-Dimensional Magnetic Recording (TDMR) system including a plurality of read heads has been developed.